1. Field of the Invention
This invention relates to the manufacture of diisopropyl ether and isopropyl alcohol, and more specifically to the indirect hydration of propylene for formation of di-isopropyl ether and isopropyl alcohol.
2. Description of the Prior Art
Large volumes of alcohols and ethers are produced annually by the catalytic hydration of olefins, in which the selected olefin feed is absorbed in a concentrated sulfuric acid stream to form an "extract" containing the corresponding alkyl ester of the sulfuric acid. Thereafter, water is admixed with the ester-containing extract to hydrolyze the ester and to form the desired alcohol and ether which are then recovered, generally by stripping with steam or some other heating fluid in an alcohol generator. There is thereby produced a diluted sulfuric acid stream which is then generally treated to concentrate it with respect to sulfuric acid for recycle to the absorption stage.
In these conventional processes, the amount of byproduct di-isopropyl ether can be increased slightly by varying the reaction condition, e.g., by increasing the ratio of reacted propylene to sulfuric acid, but a major change in di-isopropyl ether production cannot be easily realized.
U.S. Pat. No. 2,105,508 relates to a process for producing di-isopropyl ether (DIPE) by absorption of propylene. The extract liquid is passed from the absorption tower and introduced, after the addition of water or steam (to compensate for the water reacting to form the ether) to one of a series of ether generating pots, each equipped with steam coils. A vaporous product containing DIPE and the corresponding alcohol, isopropyl alcohol (IPA), is withdrawn, treated in a soda scrubber and passed to a distillation tower. Unreacted propylene is recovered as overheads in the distillation tower and can be recycled to the absorber. A sidestream of condensed ether vapors is withdrawn from the top of the distillation tower, and an IPA-containing liquor is formed as bottoms product. The alcoholic bottoms is then, with or without removal of water, refluxed to the ether generating pots or passed to further refining as alcohol. Spent acid liquor remaining in the ether generating pots is recycled to the absorber.
Reflux of the alcoholic bottoms to the ether generating pots is said to permit more accurate control of the ether generating conditions therein and to permit the acid to be concentrated to a higher strength before recycle to the absorber.
British Pat. No. 535,111 relates to a process for manufacture of ethers from olefins in which the sulfuric acid extract liquid is removed from the absorbing tower and is partially stripped in a stripping tower to form an ether-alcohol overhead mixture and a partially stripped extract as bottoms. The overhead mixture is passed to a separate tower for separation of the ether and to form an alcohol-containing bottoms. These alcohol-containing bottoms from the last tower are combined with the partially stripped extract, and sufficient water is added to make up that used in the formation of the ether. The resulting liquid stream is then recycled as the absorbate to the top of the absorbing tower.
In U.S. Pat. No. 2,216,931, aliphatic ethers such as di-isopropyl ether are produced by a process in which the sulfuric acid extract containing olefin values is split into two portions: a first portion is passed, after addition of water, to a stripping tower for formation of a vaporous overhead comprising the corresponding alcohol; and a second portion is fed directly to a reaction tower, together with the vaporous alcohol overhead formed in the stripping tower. In the reaction tower a liquid overhead stream is withdrawn and then passed to a generator for formation of vapors, which are then fed into a fractionating tower for recovery of the di-isopropyl ether product as overhead and to form a bottoms product comprising isopropyl alcohol. This alcohol bottoms is then admixed with the stream containing the alcohol vapors withdrawn from the stripping tower for feed to the reaction tower. A dilute sulfuric acid stream is withdrawn as bottoms from the generator and is then concentrated for eventual recycle to the absorbing stage.
In U.S. Pat. No. 2,533,808, the extract liquid is diluted with water and then passed to an alcohol generator for formation of dilute sulfuric acid as bottoms and to form overhead vapors comprising isopropyl alcohol and di-isopropyl ether. This vapor product is then treated to separate the isopropyl alcohol as product and to recover the di-isopropyl ether, which is recycled to the absorbing stage. In this process, the production of isopropyl alcohol can be increased by the recycle of the di-isopropyl ether.
In the process of U.S. Pat. No. 2,609,400, the propylene sulfuric acid extract liquid is stripped without dilution with water in a generator-stripper to form a mixture of ether and alcohol vapors. The partially stripped acid extract is then admixed with sufficient water (which can be added as steam via the steam injection into the stripper) to replace the water consumed in forming the alcohol and ether thus removed. Careful regulation of the extract temperature, steam temperature and pressure, and use of hot stripping gas is required to so control the heat balance of the generator-stripper to avoid dilution of the acid. Partially stripped acid extract is withdrawn from the generator-stripper and recycled to the olefin absorber, together with make-up acid as required. The ether/alcohol vapors withdrawn from the generator-stripper are scrubbed with a caustic solution to remove entrained acid, and the acid-free vapors are then condensed. The condensate, which comprises predominantly isopropyl alcohol, can be distilled to separate DIPE, which can be at least in part admixed with the partially stripped acid extract for recycle to the absorber.
In U.S. Pat. No. 2,994,721, the extract is passed into an ether generation zone from which vapors comprising predominantly di-isopropyl ether are withdrawn as overhead. The remaining liquids are then diluted with water and fed to an alcohol generator for formation of overhead vapors comprising isopropyl alcohol and some di-isopropyl ether. Again, a dilute acid is withdrawn as bottoms product from the alcohol generator for concentration and subsequent recycle to the absorbing stage.
In German Offenlegungsschrift No. 2,759,237 propylene is absorbed in sulfuric acid to form an extract which is then treated to liberate the ether and alcohol. After separation of the alcohol, the ether is recycled to make more alcohol.
None of the foregoing processes are readily adaptable to produce widely varying ratios of co-product isopropyl alcohol and di-isopropyl ether.